This invention relates to a power steering system for an outboard motor mounted on a boat, and more particularly to a power steering system for an outboard motor which is adapted to carry out the power steering of an outboard motor having an engine mounted thereon while power-assisting it by means of an electric motor.
A conventional power steering system for an outboard motor having an engine mounted thereon which has been widely known in the art is disclosed in U.S. Pat. No. 4,419,084 issued to Borst on Dec. 6, 1983.
The conventional power steering system disclosed includes a drive wheel connected to an electric motor and a driven wheel arranged in a manner to be perpendicular to a plane of the drive wheel and constantly in contact with the drive wheel. The driven wheel is arranged in a manner to be movable in the radial direction of the drive wheel, as well as movable in the above-described radial direction depending upon the angle of rotation of a steering wheel. However, the driven wheel is adapted to be contacted with the center of the drive wheel when the steering wheel is at a neutral position. Thus, when the driven wheel is in this situation, it is prevented from being rotated irrespective of the rotation of the drive wheel.
Also, the conventional power steering system includes an input shaft for supporting the driven wheel, which is connected through a gear box to a threaded rod. This causes the rotation of the input shaft due to the rotation of the driven wheel to rotate the threaded wheel. The steering angle of the outboard motor is determined depending upon the so-determined number of rotations of the threaded rod.
In the conventional power steering system constructed as described above, the rotation of the steering wheel causes the input shaft to be moved in the axial direction thereof depending upon the steering power of the steering wheel, as well as the driven wheel to be moved in the radial direction of the drive wheel, resulting in the driven wheel being offset. The amount or magnitude of offset of the driven wheel is proportional to the steering power of the steering wheel.
When the driven wheel is thus offset with respect to the drive wheel, the rotation of the drive wheel is transmitted to the driven wheel, so that an outboard motor may be steered. An increase in steering force of the steering wheel causes the amount of offset of the driven wheel to be increased correspondingly, resulting in the number of revolutions of the driven wheel being increased even when the number of revolutions of the electric motor is kept constant. In other words, this causes the steering speed of the outboard motor to be increased correspondingly.
Unfortunately, the conventional steering system lacks a control mechanism for controlling the electric motor, resulting in the electric motor having to be continuously driven so far as the operation of the steering system is continued. Also, when the amount of offset of the driven wheel is zero, only the drive wheel is rotated while the drive wheel and driven wheel are kept in contact with each other. This causes both wheels to be highly worn. An increase in wear of both wheels prevents the rotation of the drive wheel from being accurately transmitted to the driven wheel, so that the steering performance of the steering system greatly deteriorates.
In addition, the conventional power steering system fails to vary the steering force depending upon the amount or magnitude of steering reaction force, resulting in a failure in controlling the steering force so as to correspond to the steering reaction force.
Further, the conventional power steering system is complicated in the structure of its transmission mechanism for operatively connecting the steering wheel to the final output mechanism and in the large number of parts required for the transmission mechanism, thereby causing the loss of power transmission and the cost of the system to be increased, leading to deterioration of the reliability of the system.